Virgin Galactic just flew to 82.68 kilometers—is this space?

On a clear and cold Thursday morning in the Mojave Desert, Virgin Galactic's White Knight Two aircraft took off. It carried the VSS Unity spacecraft, which on its fourth powered flight, sought to make the company's highest and fastest flight ever. It succeeded.

With Mark "Forger" Stucky and C.J Sturckow piloting the vehicle, VSS Unity was dropped from White Knight Two before burning its rocket motor for 60 seconds, reaching a velocity of Mach 2.9 and soaring to an altitude of 82.68km. These were records for the company, which may begin flying space tourists in 2019.

How big of a deal is suborbital flight?

On one hand, it's difficult to get any rocket to fly high and true. Consider that Virgin Galactic was founded in 2004. It had a basic architecture at that time—an air-launched, rocket-powered spaceship based upon a proven design—and ample funding from a British billionaire. It still took 14 years for the company to make its first spaceflight.

However, suborbital flight is still relatively easy compared to an orbital flight. This is because the energy required to reach orbit, in which a spacecraft is in free fall around the planet, is about 32 times greater than the energy needed for a parabolic flight to an altitude of 100km. So be careful about drawing an equivalence between Thursday's achievement and NASA's upcoming commercial crew flights.

What is space, anyway?

This is a great question, because there is no internationally agreed upon boundary for "space." Probably the closest thing to this comes from the World Air Sports Federation, or FAI, which uses 100km (the Karman line) to delineate the boundary of space for the purposes of establishing world records. However, this organization says it is looking at lowering this boundary from 100km to 80km, due to "Recently published analyses (that) present a compelling scientific case for reduction in this altitude."

Much of the push for a lowering of the boundary has come because of work by Harvard University astrophysicist Jonathan McDowell, who has argued that orbiting objects can survive multiple perigees at altitudes around 80 to 90km and that this altitude range is consistent with the highest physical boundary of the atmosphere, the mesopause.

"I therefore suggest that a value of 80 km is a more suitable choice to use as the canonical lower ‘edge of space’ in circumstances where such a dividing line between atmosphere and space is desired," McDowell wrote in a paper published in Acta Astronautica earlier this year.

It is also worth noting that the US Air Force considered 80km the boundary of space, and it awarded astronaut wings to the pilots of the X-15 rocket plane who exceeded that altitude in the 1960s.

Astro-nots?

As a private company, Virgin Galactic can declare "space" as whatever boundary it likes, and, accordingly, it can award astronaut wings to its paying customers. (It seems unlikely that VSS Unity will be able to reach an altitude of 100km.) Really, it will come down to what those customers, and the general public, are willing to accept. Our sense is that anyone who pays $250,000 for a brief suborbital flight will probably want to have the right to call themselves astronauts.

On Wednesday, I asked "space twitter"—most of my followers on the social media site are interested in space—for their definition of space. Somewhat surprisingly in this highly unscientific poll, only 13 percent of those who responded considered 80km high enough to be "space."

Given the impending flight of Virgin Galactic's VSS Unity to, possibly, 80km, I'm genuinely curious as to whether space twitter thinks this is "space."

— Eric Berger (@SciGuySpace) December 12, 2018

Space Twitter is not alone, however, in its dismissive view toward 80km. Recently, at a party, I asked an astronaut who has flown multiple times into orbit aboard the space shuttle. He was dismissive of both 80km and the Karman line. "Orbit," he said, "is what counts."

Time will tell whether the public accepts that viewpoint, or whether seeing Virgin Galactic fly high into the atmosphere, and share photos and video of the experience, changes that perception. Either way, Thursday's flight represented a great step forward for the company—and the aspirations of the new space community.

Listing image by Virgin Galactic